Computer integrated telephony has seen developments in recent years including packet-based telephony protocols, such as Voice-over-IP, Voice-over-ATM and others. Underlying transport media may not contain commands to manage call resources, such as to connect a caller to a recipient according to network address, available route, or meter or bill the call. Digital voice path techniques therefore typically require additional services for call setup, monitoring and call teardown purposes.
One protocol capable of generating and managing packet network call resources is the Session Initiation Protocol (SIP). The SIP protocol is known in the art, and provides cell setup and management services generally analogous to those of Signaling System 7 (SS7) in the public telephony network so that end systems, proxies and other data network platforms may initiate and terminate calls or other messaging events.
Thus, SIP includes messaging for click-to-dial, call invite, ringing, recipient acknowledgment, hangup (bye) and other commands and actions generally similar to the ringing, call pickup, termination and other functions of the public switched telephone network.
In connection with the increasing computer integration of telephony functions, some devices with telephony capability may be connected to host computers via standard interfaces, such as the Universal Serial Bus (USB) promulgated by Intel Corp. and others.
Even with the advent of the ability to initiate computer-based telephone connections over the Internet or other networks using SIP or other protocols, establishing a high-quality voice path between the connected parties using VoIP or other transport media is not guaranteed. This is in part because there is no standard for guaranteeing quality of service (QoS) over public data networks like the Internet.
Consequently, there are occasions when a telephone user may prefer to place a call over the public switched telephone network because of the comparatively robust grade of voice quality in that medium. However, no mechanisms exist for SIP-based or other devices to transparently revert to POTS calls when Internet quality degrades, or to automatically attempt an Internet-based call at those times when that medium offers cost or other advantages. Other drawbacks exist.